Internal combustion engines have many components that can affect the reliable and efficient operation of the engine. Engine operation and performance may be especially affected by the condition of those components that are associated with the engine's combustion cylinders such as intake and exhaust valves, piston rings, head gaskets and the like, as well as the various sensors that provide information to one or more controllers that control the operation of various actuators on the engine. Sensor information specifically can affect the ratio of fuel and air provided to an engine cylinder during operation, which can affect the engine's performance both in terms of power as well as in terms of emissions, which, in many countries, are regulated. The reliable control of the engine's air/fuel ratio is especially important in engines operating close to a stoichiometric air/fuel ratio, such as homogeneous combustion engines.
Homogeneous combustion engines, such as engines operating with a gaseous fuel or engines operating on more than one fuel, e.g., dual fuel engines and homogeneous charge compression ignition engine, requires controlling the engine's air to fuel ratio (AFR) accurately so that the engine can provide the intended power while also meeting emission regulations. In a typical engine, the AFR is continuously calculated, in real time, based on the amount of air ingested by the engine and the amount of fuel injected directly or indirectly into the engine cylinders. In the past, an indication of the mass air flow (MAF) of an engine has been determined directly, for example, by use of dedicated MAF sensors, or indirectly, for example, by a calculation based on readings from intake-manifold pressure sensors of the engine. To control the MAF of the engine, various devices such as intake throttles have also been used. A typical intake throttle valve may be controlled by an engine Electric Control Module (ECM) to adjust the MAF. In typical engines, however, there are important technical challenges in controlling MAF effectively to this achieve a desired AFR.
One technical challenge concerns transient engine events, which, as used here, describe periods of changing speed and/or load of an engine. During a transient event, the pressure and temperature sensors that may be associated with the intake manifold and used to determine MAF, or even a MAF sensor, will take a certain period of time to update their readings of the transiently changing engine MAF. Such a time lag may depend on various factors including sampling frequency of the sensors involved, response time of those sensors, the extent and rate of the transient change in MAF, and other factors.
When operating in a transient condition, especially for engines that provide fuel to the cylinders indirectly such as by fumigation of a gaseous fuel in the engine's intake manifold, some engine controllers may command a fuel injection before the closure of an intake valve. When the intake valve closes, the MAF into the cylinder can be more accurately determined based on the profile of the MAF sensor's readings. To improve the combustion process, an engine controller may sometimes be configured to allot a preset time period before intake valve closure to inject the fuel and to permit enough time for a thorough mixing of the air and fuel. In such conditions, it can be appreciated that the MAF must be determined or estimated while the intake valve is still open, because the amount of fuel that will be delivered must depend on this estimation. In other words, a control logic for delivering a desired AFR is tasked, in known engines, with providing a MAF estimation at the beginning of fuel injection during a transient event. The accuracy of this estimation directly affects the accuracy of the resulting AFR control.
Another technical challenge is that modern engines include more than one actuated components and system that can affect AFR control. In addition to a throttle valve discussed above, a typical engine may also include an exhaust gas recirculation (EGR) valve, a compressor bypass valve, a turbine waste-gate valve, each of which can affect the amount of fresh air ingested by the engine. An AFR control must thus consider the effect valves in addition to the intake throttle valve may have on the engine MAF, and also estimate that effect to avoid errors during transient operation, when most of these other valves will be operating and changing positions.
Yet another technical challenge may arise in the event of an in-range or an out-of-range failure of one or more engine sensors contributing information to an AFR control. Whenever there is a failure of an engine sensor that is implicated in AFR control, typical engine diagnostic algorithms will identify the failure and will typically impose a limp-home or reduced-power operating mode of the engine. For certain critical tasks, a back-up engine or engines are typically utilized to ensure the continuous power supply to avoid a power drop due to an engine assuming a reduced-power mode of operation because of an engine failure. However, such measures may not be acceptable for critical engine applications, and may create inconvenience and loss of productivity even for non-critical applications.
One past attempt to address these issues can be seen in U.S. Pat. No. 7,458,361 (“Wild”). The Wild references addresses the issue of accurate MAF estimation by using a “setpoint quantity” of air, which precedes an “actual quantity” of air during transient operation. According to Wild, the setpoint quantity can be used to predict the actual quantity by correcting the setpoint quantity characterizing the setpoint air charge in such a way that the predicted quantity agrees in a steady state with an actual quantity characterizing an actual air charge, at least within a tolerance range. The Wild reference also includes providing the setpoint quantity characterizing the setpoint air charge to a first shaping network, which portrays a dynamic response of at least one region of the intake manifold, at least within a tolerance range. However, Wild discloses a single output algorithm, which can be used to control a single actuator such as an intake throttle, which would be an ineffective solution for most modern engines having additional actuators that can affect MAF such as EGR, compressor bypass, turbine waste-gate valves and the like.
Another past attempt can be seen in U.S. Pat. No. 7,814,752 (“Hu”). Hu introduces a fluid control system that can utilize the decoupled control algorithm to adjust throttle valve, EGR valve, compressor bypass valve and turbine waste-gate valve. However, the strategy used by Hu's system is almost entirely based on interpolation maps that use sensor inputs. In the event of failure of the sensor providing the information required to interpolate values on the map, the system would be rendered inoperative.
Lastly, another past attempt at addressing these issues can be seen in U.S. Patent Application Pub. No. 2012/0173118 (“Wang”). Wang describes a multiple input, multiple output (MIMO) system with coupled input-output response loops. In a typical feed forward control frame, a great amount of maps have to be populated and validated to provide accurate control for engine MAF and EGR. Wang uses model-based approaches, which include an inverse flow model or an inverse of a physical model of a system to determine those system settings required to achieve a desired flow. However, the system of Wang is still susceptible to loss of functionality in the event of a sensor failure, for example, in the position sensor or pressure sensor, because both those sensors are necessary inputs to the control strategy.